Air-fuel ratio control apparatus for internal combustion engine

Abstract

An air-fuel ratio control apparatus for an internal combustion engine has a fuel injection valve for supplying fuel to the engine, a catalytic converter disposed in an exhaust passage of the engine, and an O 2 -sensor for detecting the air-fuel ratio. Before the temperature of the catalytic converter increases to a temperature at which the catalyst is activated, a quantity of unburned fuel present in the exhaust gas is increased by increasing a fuel injection duration within an open intake valve period to a duration Longer than a fuel injection duration within the open intake valve period after activation of the catalytic device.

What is claimed is: 
     
       1. An air-fuel ratio control apparatus for an internal combustion engine, comprising: fuel injection means for supplying fuel to a combustion chamber of the internal combustion engine;   an emission-controlling catalytic device provided in an exhaust passage of the internal combustion engine;   catalytic activation determination means for determining whether the emission-controlling catalytic device is active; and   control means for, before the emission-controlling catalytic device is active, controlling fuel injection by the fuel injection means to maintain a fuel-lean ratio while increasing an amount of fuel injected during an open intake valve period during which an intake valve of the internal combustion engine is open.   
     
     
       2. An air-fuel ratio control apparatus according to claim 1, wherein, before the emission-controlling catalytic device is active, the control means controls fuel injection to maintain a fuel-lean air-fuel ratio, and controls fuel injection so that a first amount of fuel is injected during the open intake valve period, wherein the first amount of fuel is greater than a second amount of fuel injected during an open intake valve period after the emission-controlling catalytic device is active. 
     
     
       3. An air-fuel ratio control apparatus, according to claim 1, wherein, before the emission-controlling catalytic device is active, the control means delays a fuel injection end timing as compared to a fuel injection end timing set after activation of the catalytic device. 
     
     
       4. An air-fuel ratio control apparatus, according to claim 1, wherein the catalytic activation determination means includes catalyst temperature detection means for detecting a temperature of the emission-controlling catalytic device, and   wherein, before the temperature of the emission-controlling catalytic device increases to an activation temperature thereof, the control means controls fuel injection so that the amount of fuel injected during the open intake valve period increases.   
     
     
       5. An air-fuel ratio control apparatus according to claim 4, wherein, before the emission-controlling catalytic device is active, the control means delays a fuel injection end timing as compared to a fuel injection end timing set after activation of the catalytic device. 
     
     
       6. An air-fuel ratio control apparatus according to claim 1, wherein the emission-controlling catalytic device is a three-way catalytic device that reduces amounts of HC, CO and NO x  components of exhaust gas from the internal combustion engine. 
     
     
       7. An air-fuel ratio control apparatus according to claim 1, further comprising air-fuel ratio detection means for detecting an air-fuel ratio of combustion gas in the internal combustion engine, wherein, before the emission-controlling catalytic device is active, the control means controls fuel injection so that the air-fuel ratio detected by the air-fuel ratio detection means becomes a fuel-lean air-fuel ratio.   
     
     
       8. An air-fuel ratio control apparatus according to claim 7, wherein the air-fuel ratio detection means includes an O 2  -sensor. 
     
     
       9. An air-fuel ratio control apparatus according to claim 7, wherein, after the emission-controlling catalytic device is active, the control means controls fuel injection so that the air-fuel ratio detected by the air-fuel ratio detection means becomes a theoretical air-fuel ratio. 
     
     
       10. An air-fuel ratio control apparatus according to claim 1, wherein, before the emission-controlling catalytic device is active, the control means controls fuel injection to increase an amount of unburned fuel entering the exhaust passage. 
     
     
       11. An air-fuel ratio control apparatus according to claim 1, further comprising: an intake valve;   an exhaust valve; and   a variable valve timing device for varying a valve overlap period during which both the intake valve and the exhaust valve are open,   wherein, before the emission-controlling catalytic device is active, the control means controls the variable valve timing device to adjust the valve overlap period to increase an amount of unburned fuel entering the exhaust passage.   
     
     
       12. An air-fuel ratio control apparatus according to claim 11, wherein, before the emission-controlling catalytic device is active, the control means maintains a fuel-lean air-fuel ratio to increase a quantity of oxygen present in the exhaust gas, and controls the variable valve timing device so that an amount of unburned fuel entering the exhaust passage becomes greater than an amount of unburned fuel entering the exhaust passage after the emission-controlling catalytic device is active. 
     
     
       13. An air-fuel ratio control apparatus according to claim 12, wherein the control means increases the amount of unburned fuel entering the exhaust passage by increasing the valve overlap period variable by the variable valve timing device. 
     
     
       14. An air-fuel ratio control apparatus according to claim 11, wherein the catalytic activation determination means includes catalyst temperature detection means for detecting a temperature of the emission-controlling catalytic device, and   wherein, before the temperature of the emission-controlling catalytic device increases to an activation temperature thereof, the control means maintains a fuel-lean air-fuel ratio to increase a quantity of oxygen present in the exhaust gas, and controls the variable valve timing device so that the valve overlap period becomes longer than a valve overlap period occurring after the emission-controlling catalytic device is active to increase an amount of unburned fuel entering the exhaust passage.   
     
     
       15. An air-fuel ratio control apparatus according to claim 14, wherein, before activation of the catalytic device, the control means controls the variable valve timing device so that a closing timing of the exhaust valve is delayed in comparison with a closing timing of the exhaust valve set after activation of the catalytic device. 
     
     
       16. An air-fuel ratio control apparatus according to claim 1, wherein the fuel injection means injects fuel directly into a cylinder of the internal combustion engine. 
     
     
       17. An air-fuel ratio control apparatus according to claim 1, wherein the fuel injection means injects fuel into an intake port of the internal combustion engine. 
     
     
       18. An air-fuel ratio control apparatus according to claim 17, wherein the fuel injection means injects fuel at a constant injecting rate, and   wherein, when the emission-controlling catalytic device is not yet activated, the control means increases a period during which fuel is injected within the open intake valve period as compared to a period during which fuel is injected within the open intake valve period after the emission-controlling catalytic device is active, to increase a quantity of unburned fuel present in the exhaust gas.   
     
     
       19. An air-fuel ratio control apparatus for an internal combustion engine, comprising: an intake valve;   an exhaust valve;   a variable valve timing device for varying a valve overlap period during which both the intake valve and the exhaust valve are open;   fuel injection means for supplying fuel into a combustion chamber of the internal combustion engine;   an emission-controlling catalytic device provided in an exhaust passage of the internal combustion engine;   catalytic activation determination means for determining whether the emission-controlling catalytic device is active; and   control means for, before the emission-controlling catalytic device is active, controlling fuel injection to maintain a fuel-lean ratio while increasing an amount of unburned fuel in the exhaust passage by increasing a duration of the valve overlap period via the variable valve timing device.